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GC Technical Tip

Basic Considerations for High Temperature GC

A Technical Tip by Kristen Parnell, GC Brand Manager

In gas chromatography, elevated oven temperatures can be used to elute high boiling analytes faster with improved peak shapes, leading to better quantitation. Temperature ramps at the end of an analysis can be used to remove contaminants that may lead to various analytical problems including premature column death. Below are some hints and tips to consider when performing high temp analysis.

1. Ensuring Proper Column Selection
Both fused silica and metal columns can be used when running at high temperatures. Metal columns (example: ZB-1XT SimDist) are extremely rugged and offer the highest temperature limits. However, metal columns may be more rigid and slightly more difficult to install. Typically, high temperature stable fused silica columns (examples: ZB-1HT, ZB-5HT, ZB-35HT, ZB-XLB-HT) provide good performance while maintaining flexibility and easy column installation. Fused silica columns that are not high temperature rated may become brittle or damaged after repeated exposures. Choose a column which best suits the stability, temperature, and ease of use needs for your analysis.

2. Managing Thermally Labile Compounds
In hot inlets, thermally labile analytes are prone to decomposition in the presence of the high temperatures required for fast sample vaporization. When dealing with thermally labile compounds, balancing lower peak areas (because of higher temperatures) with longer retention times (caused by lowering temperatures) is the key to mitigating this decomposition. Using on-column injection, columns with thinner stationary phases, shorter column lengths, and higher carrier gas flow rates can help elute compounds at slightly lowered temperatures and therefore minimize breakdown. Learn more on thermally labile compounds here.

3. “Baking Out” Your Column
Column contamination and performance degradation can happen if high boilers are not eluted with each run. The final oven temp must be high enough to ensure elution of these compounds, but not so high that thermal damage occurs. This can be done either isothermally or with an oven ramp until the last compounds elute from the column.

Never exceed the upper temperature limits of your column. Severe degradation and stationary phase loss, as well as permanent damage to the column tubing can result. Chromatographically, this can present as excessive column bleed, peak tailing, decreased resolution, shortened run times, reduced column lifetimes or even column failure. To prevent accidental overheating and thermal damage to your column, set the oven’s maximum temperature at, or slightly below, the column’s upper temperature limit.

Don’t exceed more than 15 minutes at upper isothermal temperature limits specified for your column. Baking out your column may cause irreversible damage if contaminants are chemically converted to insoluble materials that can no longer be removed, even by solvent rinsing. The best way to guard against column contamination and performance degradation is to carefully and thoroughly extract and filter your samples. Before baking your column out, try solvent rinsing first.

4. Using Compatible High Temperature Accessories
The choice of liners, ferrules, septa, inlet base seals and even press-fit guard columns should be made with high temperature runs in mind. Oxygen contamination due to leaky inlet seals can cause significant column damage or even column failure at high temperatures. Septum bleed from coring or the use of septa not suitable for high temperature use may result in degraded chromatographic results. Choosing the appropriate accessories for your analysis will help ensure the best performance for your column and system. Learn more about high temperature accessories here.